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-rw-r--r--diffcore-break.c127
1 files changed, 127 insertions, 0 deletions
diff --git a/diffcore-break.c b/diffcore-break.c
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+/*
+ * Copyright (C) 2005 Junio C Hamano
+ */
+#include "cache.h"
+#include "diff.h"
+#include "diffcore.h"
+#include "delta.h"
+#include "count-delta.h"
+
+static int very_different(struct diff_filespec *src,
+ struct diff_filespec *dst,
+ int min_score)
+{
+ /* dst is recorded as a modification of src. Are they so
+ * different that we are better off recording this as a pair
+ * of delete and create? min_score is the minimum amount of
+ * new material that must exist in the dst and not in src for
+ * the pair to be considered a complete rewrite, and recommended
+ * to be set to a very high value, 99% or so.
+ *
+ * The value we return represents the amount of new material
+ * that is in dst and not in src. We return 0 when we do not
+ * want to get the filepair broken.
+ */
+ void *delta;
+ unsigned long delta_size, base_size;
+
+ if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
+ return 0; /* leave symlink rename alone */
+
+ if (diff_populate_filespec(src, 1) || diff_populate_filespec(dst, 1))
+ return 0; /* error but caught downstream */
+
+ delta_size = ((src->size < dst->size) ?
+ (dst->size - src->size) : (src->size - dst->size));
+
+ /* Notice that we use max of src and dst as the base size,
+ * unlike rename similarity detection. This is so that we do
+ * not mistake a large addition as a complete rewrite.
+ */
+ base_size = ((src->size < dst->size) ? dst->size : src->size);
+
+ /*
+ * If file size difference is too big compared to the
+ * base_size, we declare this a complete rewrite.
+ */
+ if (base_size * min_score < delta_size * MAX_SCORE)
+ return MAX_SCORE;
+
+ if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
+ return 0; /* error but caught downstream */
+
+ delta = diff_delta(src->data, src->size,
+ dst->data, dst->size,
+ &delta_size);
+
+ /* A delta that has a lot of literal additions would have
+ * big delta_size no matter what else it does.
+ */
+ if (base_size * min_score < delta_size * MAX_SCORE)
+ return MAX_SCORE;
+
+ /* Estimate the edit size by interpreting delta. */
+ delta_size = count_delta(delta, delta_size);
+ free(delta);
+ if (delta_size == UINT_MAX)
+ return 0; /* error in delta computation */
+
+ if (base_size < delta_size)
+ return MAX_SCORE;
+
+ return delta_size * MAX_SCORE / base_size;
+}
+
+void diffcore_break(int min_score)
+{
+ struct diff_queue_struct *q = &diff_queued_diff;
+ struct diff_queue_struct outq;
+ int i;
+
+ if (!min_score)
+ min_score = DEFAULT_BREAK_SCORE;
+
+ outq.nr = outq.alloc = 0;
+ outq.queue = NULL;
+
+ for (i = 0; i < q->nr; i++) {
+ struct diff_filepair *p = q->queue[i];
+ int score;
+
+ /* We deal only with in-place edit of non directory.
+ * We do not break anything else.
+ */
+ if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
+ !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) &&
+ !strcmp(p->one->path, p->two->path)) {
+ score = very_different(p->one, p->two, min_score);
+ if (min_score <= score) {
+ /* Split this into delete and create */
+ struct diff_filespec *null_one, *null_two;
+ struct diff_filepair *dp;
+
+ /* deletion of one */
+ null_one = alloc_filespec(p->one->path);
+ dp = diff_queue(&outq, p->one, null_one);
+ dp->score = score;
+ dp->broken_pair = 1;
+
+ /* creation of two */
+ null_two = alloc_filespec(p->two->path);
+ dp = diff_queue(&outq, null_two, p->two);
+ dp->score = score;
+ dp->broken_pair = 1;
+
+ free(p); /* not diff_free_filepair(), we are
+ * reusing one and two here.
+ */
+ continue;
+ }
+ }
+ diff_q(&outq, p);
+ }
+ free(q->queue);
+ *q = outq;
+
+ return;
+}